This invention relates to newly identified polynucleotide sequences, polypeptides encoded by such sequences, the use of such polynucleotides and polypeptides, as well as the production of such polynucleotides and polypeptides. More particularly, the polypeptides of the present invention are three human DNA mismatch repair proteins, HMLH1, HMLH2, and HMLH3.
In both procaryotes and eucaryotes, DNA mismatch repair plays a prominent role in the correction of errors made during DNA replication and genetic recombination. The E.coli methyl-directed DNA mismatch repair system is the best understood DNA mismatch repair system to date. In E.coli, this repair pathway involves the products of the mutator genes mutS, mutL, mutH, and uvrD. Mutants of any one of these genes will reveal a mutator phenotype. MutS is a DNA mismatch-binding protein which initiates this repair process, UvrD is a DNA helicase and MutH is a latent endonuclease that incises at the unmethylated strands of hemimethylated GATC sequence. MutL protein is believed to recognize and bind to the mismatch-DNA-MutS-MutH complex to enhance the endonuclease activity of MutH protein. The proteins of the present invention are human mutL homologs, namely, HMLH1, HMLH2 and HMLH3. After the unmethylated DNA strand is cut by the MutH, single-stranded DNA-binding protein, DNA polymerase III, exonuclease I and DNA ligase are required to complete this repair process (Modrich P., Annu. Rev. Genetics, 25:229-53 [1991]).
Elements of the E.coli MutLHS system appears to be conserved during evolution in procaryotes and eucaryotes. Genetic study analysis suggests that Saccharomyces cerevisiae has a mismatch repair system similar to the bacterial MutLHS system. In S. cerevisiae, at least two MutL homologs, PMS1 and MLH1, have been reported. Mutation of either one of them leads to a mitotic mutator phenotype (Prolla et al, Mol. Cell. Biol. 14:407-415 [1994]). At least three MutS homologs have been found in S.cerevisiae, MSH1, MSH2, and MSH3. Disruption of the msh2 gene (affects nuclear mutation rates. Mutants S. cerevisae msh2, pms1, and mlh1 have found to exhibit increased rates of expansion and contraction of dinucleotide repeat sequences (Strand et al., Nature, 365:274-276 [1993]).
It has been reported by various laboratories that a number of human tumors such as lung cancer, prostate cancer, ovarian cancer, breast cancer, colon cancer and stomach cancer show instability of repeated DNA sequences (Han et al., Cancer, 53:5087-5089 [1993]; Thibodeau et al., Science 260:816-819 [1993]; Risinger et al., Cancer 53:5100-5103 [1993]). This phenomenon suggested that lack of the DNA mismatch repair is probably the cause of these tumors. Little is known about the DNA mismatch repair system in humans until recently, the human homolog of the MutS was cloned and found to be responsible for hereditary nonpolyposis colon cancer (HNPCC), (Fishel et al., Cell, 75:1027-1038 [1993] and Leach et al., Cell, 75:1215-1225 [1993]). The HNPCC was first linked to a locus at chromosome 2p16 which causes dinucleotide instability. It was then demonstrated that a DNA mismatch repair protein (MutS) homolog, was located at this locus and Cxe2x86x92T transitional mutations at several conserved regions were specifically observed in HNPCC patients.
It has previously been demonstrated that hereditary colon cancer can result from mutations in several loci. Familial adenomatosis polyposis coli (APC) linked to a gene on chromosome 5 is responsible for a small minority of hereditary colon cancer. Hereditary colon cancer is also associated with Gardner""s syndrome, Turcot""s syndrome, Peutz-Jaeghers syndrome and juvenile polyposis coli. In addition, hereditary non polyposis colon cancer (HNPCC)may be involved in 5% of all human colon cancer. All of the different types of familial colon cancer have been shown to be transmitted by a dominant autosomal mode of inheritance.
In addition to localization of HNPCC in two families to the short arm of chromosome 2, a second locus has been linked to a predisposition to HNPCC (Lindholm et al., Nature Genetics, 5:279-282, 1993). A strong linkage was demonstrated between a polymorphic marker on the short arm of chromosome 3 and the disease locus. It was also suggested that these families show signs of a general defect in the DNA repair process.
This finding suggests that mutations on various DNA mismatch repair proteins probably play crucial role in causing human hereditary diseases and cancers such as lung cancer, prostate cancer, ovarian cancer, breast cancer, colon cancer and stomach cancer.
In accordance with one aspect of the present invention, there is provided three novel polypeptides which are human cDNA mismatch repair proteins, sometimes hereinafter referred to as HMLH1, HMLH2 and HMLH3, as well as analogs and derivatives thereof. The polypeptides of the present invention are of human origin.
In accordance with another aspect of the present invention, there is provided a polynucleotide (DNA) which encodes such polypeptide.
In accordance with still another aspect of the present invention, there is provided a procedure for producing such polypeptide by recombinant techniques.
In accordance with yet a further aspect of the present invention, there is provided a process for using the polypeptide or DNA sequence encoding such polypeptide for diagnostic and therapeutic purposes.
These and other aspects of the present invention should be apparent to those skilled in the art from the teachings herein.
The following drawings are illustrative of embodiments of the invention and are not meant to limit the scope of the invention as encompassed by the claims.